1. Field of the Invention
The present invention relates to a broadband optical spectrum generating apparatus and a pulsed light generating apparatus. More specifically the invention pertains to a broadband optical spectrum generating apparatus that generates a broadband optical spectrum as well as to a pulsed light generating apparatus that generates pulsed light having a desired wavelength in a predetermined wavelength band.
2. Description of the Prior Art
Widely broadened optical spectra called super continuum have recently drawn attention in the field of optical communication and optical measurement. A diversity of broadband optical spectrum generating apparatuses and techniques have been proposed to utilize optical fibers having nonlinear effects and thereby generate the super continuum (for example, JAPANESE PATENT LAID-OPEN GAZETTE No. 8-234249, No. 10-90737, No. 11-160744, and No. 11-174503).
Optical fibers of several hundred meters or even several kilometers are, however, required in such prior art broadband optical spectrum generating apparatuses and techniques, and are thus unpractical. Multiple amplification stages are required for excitation light, which is used for generation of super continuum. This results in undesirably complicated construction and large size of the apparatus. Additionally, the generated spectrum has a band of only approximately 1400 nm to 1700 nm.
The object of the present invention is thus to generate an optical spectrum of a broader band or more specifically a relatively flat super continuum over a broadband in a broadband optical spectrum generating apparatus. The object of the present invention is also to attain size reduction and simplified construction of the broadband optical spectrum generating apparatus. The broadband optical spectrum generating apparatus of the invention aims at generating pulsed light of an arbitrary wavelength out of a wide wavelength band.
In order to achieve at least a part of the aforementioned objects, a broadband optical spectrum generating apparatus and a pulsed light generating apparatus of the present invention are structured as follows.
A broadband optical spectrum generating apparatus of the invention generates a broadband optical spectrum, the broadband optical spectrum generating apparatus including: a short pulse light source that emits pulsed light at a short interval; and a broadband optical spectrum-generating optical fiber that has a non-linear coefficient of not less than 10 [Wxe2x88x921 mxe2x88x921] at a wavelength of the pulsed light emitted from the short pulse light source and converts the pulsed light input from the short pulse light source into the broadband optical spectrum.
The broadband optical spectrum generating apparatus of the invention uses the broadband optical spectrum-generating optical fiber having a non-linear coefficient of not less than 10 [Wxe2x88x921mxe2x88x921], thus generating an optical spectrum over a broad band of approximately 1200 nm to 2000 nm. The broadband optical spectrum generating apparatus has the single short pulse light source. This arrangement effectively reduces the size and simplifies the structure of the whole broadband optical spectrum generating apparatus.
In the broadband optical spectrum generating apparatus of the invention, the broadband optical spectrum-generating optical fiber may be related to have a length of not greater than 50 m or preferably a length of not greater than 10 m. This arrangement ensures output of a more stable broadband optical spectrum. The broadband optical spectrum-generating optical fiber may be regulated to have a magnitude of chromatic dispersion of not greater than 2 [ps/km/nm] or preferably a magnitude of chromatic dispersion of not greater than 1.5 [ps/km/nm]. This arrangement ensures output of an optical spectrum of a broader band. One preferable example of the broadband optical spectrum-generating optical fiber may be a polarization maintaining optical fiber. This arrangement gives the broadband optical spectrum-generating optical fiber that stably having a high non-linearity, thus generating a more stable broadband optical spectrum.
In the broadband optical spectrum generating apparatus of the invention, the short pulse light source may output the pulsed light having a central wavelength of output pulse in a vicinity of 1556 nm and a pulse width in a unit of picosecond to femtosecond. The output pulsed light preferably has a narrower pulse width and a higher peak output. One desirable example of the short pulse light source may output the pulsed light having a pulse width of 10 to 1000 femtoseconds and a mean output of not less than 20 mW. This arrangement ensures generation of a more stable broadband super continuum.
In the broadband optical spectrum generating apparatus of the invention, the broadband optical spectrum may be relatively flat over a band of 1300 nm to 1900 nm. Here the state xe2x80x98relatively flatxe2x80x99 means that the output spectrum has a continuous wavelength and no significant variation in intensity.
In the broadband optical spectrum generating apparatus of the invention, there may be provided with a lens that is interposed between the short pulse light source and the broadband optical spectrum-generating optical fiber to make the pulsed light from the short pulse light source enter the broadband optical spectrum-generating optical fiber. This arrangement enables the pulsed light emitted from the short pulse light source to readily enter the broadband optical spectrum-generating optical fiber.
A pulsed light generating apparatus of the invention generates pulsed light of a desired wavelength in a preset wavelength band, the pulsed light generating apparatus including: broadband optical spectrum generation section including a short pulse light source that emits pulsed light at a short interval, and a broadband optical spectrum-generating optical fiber that has a non-linear coefficient of not less than 10 [Wxe2x88x921mxe2x88x921] at a wavelength of the pulsed light emitted from the short pulse light source and converts the pulsed light input from the short pulse light source into a broadband optical spectrum; and optical spectrum extraction section that receives a supply of the broadband optical spectrum from the broadband optical spectrum generation section and extracts an optical spectrum of an arbitrary wavelength from the received broadband optical spectrum.
In the pulsed light generating apparatus of the present invention, the optical spectrum extraction section may extract an optical spectrum of an arbitrary wavelength in the broadband optical spectrum output from the broadband optical spectrum generation section. This arrangement ensures generation of an optical spectrum of a desired wavelength, that is, pulsed light, over the broad band. The broadband optical spectrum generation section has the identical structure with that of the broadband optical spectrum generating apparatus of the invention discussed above and accordingly has the same effects as those of the broadband optical spectrum generating apparatus of the invention.
In the pulsed light generating apparatus of the invention, the optical spectrum extraction section may be a tunable filter that varies a wavelength of transmitted light. In another example, the optical spectrum extraction section may include an extracted wavelength regulator that regulates the extracted wavelength in response to an electric signal. This structure allows the wavelength of the generated pulsed light to be freely regulated.
The broadband optical spectrum-generating optical fiber used for the pulsed light generating apparatus of the invention may be regulated to have a length of not greater than 50 m or preferably to have a length of not greater than 10 m. This arrangement ensures output of a more stable broadband optical spectrum. The broadband optical spectrum-generating optical fiber may be regulated to have a magnitude of chromatic dispersion of not greater than 2 [ps/km/nm] or preferably a magnitude of chromatic dispersion of not greater than 1.5 [ps/km/nm]. This arrangement ensures output of an optical spectrum of a broader band. One preferable example of the broadband optical spectrum-generating optical fiber may be a polarization maintaining optical fiber. This arrangement gives the broadband optical spectrum-generating optical fiber that stably having a high non-linearity, thus generating a more stable broadband optical spectrum.
In the pulsed light generating apparatus of the invention, the short pulse light source may output the pulsed light having a central wavelength of output pulse in a vicinity of 1556 nm and a pulse width in a unit of picosecond to femtosecond. The output pulsed light preferably has a narrower pulse width and a higher peak output. One desirable example of the short pulse light source may output the pulsed light having a pulse width of 10 to 1000 femtoseconds and a mean output of not less than 20 mW. This arrangement ensures generation of a more stable broadband super continuum.
A short pulse light source of the invention is included in a broadband optical spectrum generating apparatus, which generates a broadband optical spectrum, and emits pulsed light to a broadband optical spectrum-generating optical fiber, which converts the pulsed light into the broadband optical spectrum, the short pulse light source outputting the pulsed light having a central wavelength of output pulse in a vicinity of 1556 nm and a pulse width in a unit of picosecond to femtosecond.
The short pulse light source of the invention is desirably applied to the broadband optical spectrum generating apparatus to generate a broadband optical spectrum.
A broadband optical spectrum-generating optical fiber of the invention is included in a broadband optical spectrum generating apparatus, which generates a broadband optical spectrum, and converts pulsed light input from a short pulse light source into the broadband optical spectrum, the broadband optical spectrum-generating optical fiber having a non-linear coefficient of not less than 10 [Wxe2x88x921mxe2x88x921] at a wavelength of the pulsed light emitted from the short pulse light source.
The broadband optical spectrum-generating optical fiber of the invention is desirably applied to the broadband optical spectrum generating apparatus to generate a broadband optical spectrum.
The broadband optical spectrum-generating optical fiber of the invention may be related to have a length of not greater than 50 m or preferably a length of not greater than 10 m. This arrangement ensures output of a more stable broadband optical spectrum. The broadband optical spectrum-generating optical fiber may be regulated to have a magnitude of chromatic dispersion of not greater than 2 [ps/km/nm] or preferably a magnitude of chromatic dispersion of not greater than 1.5 [ps/km/nm]. This arrangement ensures output of an optical spectrum of a broader band. One preferable example of the broadband optical spectrum-generating optical fiber may be a polarization maintaining optical fiber. This arrangement gives the broadband optical spectrum-generating optical fiber that stably having a high non-linearity, thus generating a more stable broadband optical spectrum.